This invention relates to a starter with a magnet type D.C. motor which has planetary reduction gears installed on the end part of an output shaft thereof.
FIG. 1 shows a prior-art starter of this type. Referring to the figure, the starter 1 has a magnet type D.C. motor 2 which is fixed to a bracket 3 by through bolts, not shown. Numeral 4 designates a tubular yoke, and a plurality of poles 5 made of ferrite permanent magnets are fastened to the inner peripheral surface thereof with an adhesive. Numeral 6 designates an intermediate bracket, which is fitted on the inner peripheral surface of the yoke 4 along with a ring gear 7. The intermediate bracket 6 supports the output end part of the rotary shaft 10 of an armature 9 through a sleeve bearing 8 which is fitted on the inner peripheral surface of a cylindrical protrusion 6a provided centrally of the intermediate bracket. An armature core 11 is fitted on the rotary shaft 10, an armature coil 12 is wound in the slots (not shown) of the armature core 11, a commutator 13 is connected to the armature coil 12, a brush 14 energizes the armature 9 in sliding contact with the commutator 13, and a bind 15 is mounted on the armature coil 12. In addition, a rear bracket 16 is fitted on a socket portion 4a provided at the rear end of the yoke 4, while a sleeve bearing 17 is fitted on a protrusion 16a provided centrally of the rear bracket 16 and supports the rear end of the rotary shaft 10. Numeral 18 indicates a cap for sealing the rear end part, and numerals 19, 20 and 21 indicate thrust washers. Further, a spur gear 22 is formed at the front end part of the rotary shaft 10 and has a planet gear 23 held in mesh therewith. A sleeve bearing 24 is fitted on the inner peripheral surface of the planet gear 23, and it is supported by a supporting pin 27 which is fitted on the housing 26 of an overrunning plutch 25. Numeral 28 indicates a roller, and numeral 29 a clutch-inner. A rotary output shaft 30 is fastened to the clutch-inner 29, and has a pinion 32 spline-fitted with a helical spline 31 which is formed in the outer peripheral surface of the rotary output shaft. Numeral 33 denotes a washer, and numeral 34 a cover which unitarily fastens the housing 26, roller 28 and clutch-inner 29 in engagement through the washer 33. A washer 35 fastens a link 36 in engagement with the pinion 32, and a shift lever 37 is brought into cam engagement with the link 36 so as to shift the pinion 32 frontwards. A sleeve bearing 38 is fitted in a recess 29a provided in the inner peripheral surface of the clutch-inner 29, and supports the front end part of the rotary shaft 10. A spacer 39 is fastened in engagement with the end face of the tooth portion of the ring gear 7, and is mounted in the state in which it is held between the front bracket 3 and the yoke 4.
The prior-art starter 1 operates as described below. When the shift lever 37 is turned by means of an electromagnetic switch, not shown, the pinion 32 is shifted frontwards on the spline 31 of the rotary output shaft 30 and meshes with the ring gear of an internal combustion engine, not shown. Thereafter, when the main contact (not shown) of the aforementioned electromagnetic switch is closed, a supply voltage is applied to the brush 14, and the armature 9 is energized to generate a turning force. The turning force of the armature is transmitted to the spur gear 22 on the rotary shaft 10, and is further transmitted to the overruning clutch 25 through the pin 27 after the turning speed of the spur gear has been decelerated by the planet gear 23. Owing to the resultant turning force, the pinion 32 is urged to rotate in one direction through the roller 28, clutch-inner 29 and helical spline 31 on the rotary output shaft 30. Thus, the internal combustion engine is started.
Since the prior-art starter is constructed and operated as described above, particularly the poles 5 for magnetically driving the armature 9 suffer great magnetic reactions, and the yoke 4 and the poles 5 need to be firmly bonded in order to ensure a strength high enough to withstand the reactions. Moreover, since the intermediate bracket 6 and the ring gear 7 are fitted on the inner peripheral surface of the yoke 4, the assembling job of the starter is complicated. Another disadvantage is that the number of constituent parts becomes large.